1. Technical Field
The present invention relates to an image reading device, a correction method applied in the image reading device, and to an image processing method using the image reading device.
2. Related Art
Technology for reading images using a scanner or other type of image reading device, applying various image processing techniques (such as correcting shading or gamma correction) to the image data of a scanned image, and then outputting the corrected image data to an external device such as a personal computer, is known from the literature. Such scanners typically have memory (such as SDRAM (Synchronous Dynamic Random Access Memory)) for storing the image data before an image data correction process is applied and correction data used for the image data correction process. Japanese Unexamined Patent Appl. Pub. JP-A-2008-192262, for example, teaches technology related to SDRAM control.
Technology for correcting the image data captured by the scanner or other image reading device, such as correcting skewed images, and outputting the corrected image data is also known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2001-119541 and Japanese Unexamined Patent Appl. Pub. JP-A-2002-514366.
Such an image reading device with SDRAM according to the related art reads the correction data from the same bank as the bank to which the image data is written and read. If an area specified by a different row address in the same bank is accessed on a time-share basis, a precharge is required each time the memory is accessed and the memory data transfer rate drops.
This problem is not limited to image reading devices with SDRAM, and is generally common to all types of image reading devices having memory with a plurality of banks.
The invention is directed to solving this problem by providing technology that improves the transfer rate of memory disposed in an image reading device.
There are also image reading devices that convey paper on which images are formed and use a plurality of imaging elements arrayed in a line to read the image and produce image data. By using only every n-th imaging element in a row of imaging elements, image data with lower resolution than when all imaging elements are used can be produced.
Such image reading devices may also correct shading in the image data of a captured image by using white and black reference data values (collectively referred to below as “reference data values”) for each imaging element. These reference data values are stored in advance in memory in the image reading device.
However, when the image reading device produces low resolution image data and then corrects the shading of the image data, the reference data values needed for the correction must be selected while being read. As a result, the reference data cannot be retrieved at high speed. More particularly, while data can be read quickly using a burst access mode when SDRAM is used as the memory of the image reading device, burst access cannot be used effectively when the reference data required for correction is stored in non-contiguous areas, and the reference data transfer rate drops accordingly. This problem is not limited to shading correction, and is common to all image data correction processes according to the characteristics of the imaging elements of the image reading device.